Control of Plant-Parasitic Nematodes (1968) / Chapter Skim
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BASIC PRINCIPLES OF CONTROL
BASIC PRINCIPLES OF CONTROL
Pages 85-166
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From page 85... ...
MEANS OF DISSEMINATION SOIL AND PLANT TISSUE Soil and vegetative plant parts, because they often protect nematodes from desiccation and are frequently transported by man, are important carriers of nematodes over both short and long distances. Soil is also important because most plant-pathogenic nematodes spend at least part of their lives in soil, and soil thus infested is commonly transported along with plant materials.
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From page 86... ...
Since these highacre-value plants are cultivated on the best soil available, one crop is grown frequently or continuously on the same land, often resulting in damaging nematode populations in plant materials and in the soil. Infected propagation materials are particularly important in nematode spread, because materials from a relatively small area are used to plant much larger and often widely separated areas.
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From page 87... ...
In coarse-textured soils of Florida citrus orchards, spread of the burrowing nematodes (Radopholus similis) downhill in surface-drainage water was eight times the rate of uphill movement.
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From page 88... ...
Infested soil may be carried along with both host and nonhost plants. If the climate is unsuitable, an introduced nematode species either will not survive or its population increase will be so slow that it will not become an economically important pest.
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From page 89... ...
For example, hot water is used to treat garlic bulbs infected with stem nematodes, grape rootstocks infected with root-knot and lesion nematodes, and citrus rootstocks infected with burrowing nematode and citrus nematode (Tylenchulus semipenetrans) (Figure 40)
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From page 90... ...
Vegetative seed of banana free of the burrowing nematode, potato seed pieces free of the golden nematode, garlic cloves free of the stem nematode, and strawberry plants free of root-knot and lesion nematodes are produced commercially. The use of resistant or immune plant varieties also reduces nematode spread.
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From page 91... ...
quarantine prohibits the movement of root crops from the regulated areas where they are grown, but it also provides that root crops (except sugar beets) may be exempted "if cleaned free of soil." The prohibition of movement is a quarantine measure, while the provision for cleaning the root crops is a regulation allowing free movement of plant materials freed of the pest.
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From page 92... ...
Regulations may place stringent controls over every aspect of the growing of crops to prevent the possibility of spread of nematode pests. The New York State Golden Nematode Act of 1947 placed the planting, growing, and harvesting of potatoes under the direction of the project administrator and included regulations relating to crop rotation, topsoil movement, and soil treatment.
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From page 93... ...
Plant Quarantine Act and subsequent regulations and quarantines, federal port and border inspections annually intercept numerous important plant-pathogenic nematodes. During the fiscal year 19641965, the golden nematode was intercepted 101 times; the oat cyst nematode (Heterodera avenae)
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From page 94... ...
With the advance of knowledge of the effect of specific practices on nematode populations and with more efficient implementation of practices, for example, through improved machinery, a high degree of control may be possible. Because of this possibility, those practices that are known to reduce nematode populations to a measurable extent are discussed even though they may not be economically feasible or widely used at this time.
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From page 95... ...
Therefore, in the absence of a host plant, the nematode will die after the stored food in the body has been depleted. Some of the cyst nematodes (Heterodera spp.)
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From page 96... ...
Populations of some nematode species may decline on cover crops, but others undoubtedly increase. A reduction in population is probably caused by resistance of the cover crop to the particular nematode, and, conversely, any increase is due to susceptibility of the crop to the species that increased.
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From page 97... ...
To be an effective control practice, crops that are unfavorable hosts for the nematode must be included in the rotation sequence. Some of the more serious nematode pathogens, such as the golden nematode of potatoes (Heterodera rostochiensis)
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From page 98... ...
98 BASIC PRINCIPLES OF CONTROL FIGURE 41 The effect of crop rotation on the control of a rootknot nematode (Meloidogyne incognita) on tobacco.
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From page 99... ...
LAND-MANAGEMENT AND CULTURAL PRACTICES 99 FIGURE 42 The effect of crop rotation on the control of a rootknot nematode (Meloidogyne hapla) on peanut.
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From page 100... ...
100 BASIC PRINCIPLES OF CONTROL • I FIGURE 43 The effect of crop rotation on the control of the soybean cyst nematode (Heterodera glycines) on soybeans.
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From page 101... ...
In most cases, increased activity of microorganisms in the soil followed these treatments, and reductions in nematode populations were assumed to be caused by the buildup of nematode-destroying organisms in the soil. However, in few cases were the actual factors responsible for killing the nematodes determined.
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From page 102... ...
Two control principles are utilized in this practice: the destruction of the host plant by cutting the stalk and uprooting the plant, thus preventing further reproduction of the nematode; and the killing by desiccation of large numbers of nematodes concentrated in the soil around the root system and inside the roots. TRAP AND ANTAGONISTIC CROPS Early investigators, employing the trap-crop principle in attempts to control certain species of the cyst and root-knot nematodes, planted highly suscep
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From page 103... ...
Crotalaria has been successfully used to reduce populations of certain species of root-knot nematodes. Roots of certain plant species have recently been found to exude toxic chemicals, thus reducing the soil-population levels of some nematode species.
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From page 104... ...
SANITATION AND USE OF NEMATODE-FREE PLANTING STOCK The land-management and cultural practices discussed above reduce nematode populations in fields to varying degrees. Most of these measures have limitations: the degree of control is erratic, and sometimes those factors actually responsible for the reduction in nematode populations are not fully understood.
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From page 105... ...
Without this, selection of crops to use in a rotation sequence designed to reduce the nematode population will mostly be guesswork. The second objective, the acceleration of the death rate in the soil of nematodes neither feeding nor reproducing, but merely persisting, will depend on knowledge of the effect on nematode survival of soil environment or cultural practices applied to the soil.
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From page 106... ...
FUNGI Over 50 species of fungi capture and consume nematodes. Of these fungi, only those included in several genera of the Hyphomycetes and the Zoopagales have received attention as biological control agents.
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From page 107... ...
This predacious fungus occurs commonly in the rhizosphere of nematode-infested citrus plants. high specificity between host and parasite, or predator, are necessary if fungal traps are to be important in controlling nematodes.
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From page 108... ...
In citrus orchards, three or four species of nematode-trapping fungi are frequently intimately associated with infestations of the citrus nematode (Tylenchulus semipenetrans)
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From page 109... ...
Other soil protozoa probably have only an incidental predatory relationship to nematodes. OTHER NEMATODES Certain carnivorous nematode species, including many of the Mononchidae, comprise one of the most important and least studied groups of organisms predacious on soil and plant-parasitic nematodes.
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From page 110... ...
OTHER INVERTEBRATES Tardigrades, small animals found chiefly in water films surrounding leaves of terrestrial mosses and lichens, but sometimes numerous in the soil, will kill nematodes. Despite recent study of the role of tardigrades in soil-nematode population dynamics, relatively little is known of the biology of these curious organisms.
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From page 111... ...
In addition, the presence of decomposing organic materials in the soil apparently provides host plants with some tolerance to nematode attack. Decomposition products of organic matter and plant residues may also be detrimental, directly or indirectly, to plant-parasitic nematodes.
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From page 112... ...
The combining of chemical and biological control measures offers advantages such as reduced cost for nematocidal chemicals and reduced problems of pesticide residues. The search should continue for more specific parasites of injurious nematodes: parasites able to persist in soil, parasites able to attack endoparasitic nematodes and continue their lethal activities after the nematodes escape the soil environment and enter the host roots, and, finally, effective parasites obtainable by man in large numbers for wide dissemination in agricultural soils.
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From page 113... ...
; clover and alfalfa resistant to the stem nematode (Ditylenchus dipsaci) ; potatoes resistant to the golden nematode (Heterodera rostochiensis)
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From page 114... ...
FIGURE 49 Comparison of cyst nematode-resistant and susceptible soybean varieties in soil infested with soybean cyst nematodes (Heterodera glycines)
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From page 115... ...
Resistance is usually relative or incomplete; therefore, selection of resistant and susceptible plants, either by nematode increase or by degree of plant damage, is often difficult in breeding programs. DEVELOPMENT OF NEW VARIETIES Although a few nematode-resistant plant varieties have been developed by selection from commercial varieties, such as a Swedish red clover resistant to the stem nematode, the most common method of obtaining resistant varieties is to cross plants having desirable commercial characters with those possessing nematode resistance.
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From page 116... ...
claytoni) can be produced on callus-tissue cultures under aseptic conditions, for most ectoparasitic root feeders the only practical method is to test resistance in the field or greenhouse in soil infested by more than one nematode species.
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From page 117... ...
A resistant variety is a poor host and does not support high nematode populations. Many levels of plant resistance occur, varying from immune plants on which no nematodes develop to those supporting populations almost as high as susceptible varieties.
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From page 118... ...
Infection by stem nematodes causes conspicuous enlargement and separation of parenchymatous cells in susceptible plants but only slight cell enlargement and separation in resistant plants. Nematode populations around the roots of resistant plants sometimes decline at a more rapid rate than can be explained by starvation, and it is presumed that toxins of plant origin are responsible.
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From page 119... ...
However, a negative correlation exists between potassium levels and development of lesion nematodes in cherry. The apparent discrepancy may be explained by the levels of potassium used, duration of the experiment, plant species used, or nematode species used.
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From page 120... ...
Resistance caused by a specific plant gene has been found responsible for resistance to one to four nematode species. RESISTANCE TO COMPLEX DISEASES In plant-breeding programs to control disease caused by nematodes and microorganisms such as fungi or bacteria, it is important to breed for resistance to all organisms but particularly for nematode resistance.
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From page 121... ...
Progress in breeding for resistance to root knot increased rapidly after the root-knot nematodes were separated into a number of species differing in host range. The high cost of direct control measures, and persistence of nematodes in the soil, point to a need for emphasis on breeding resistant varieties of plants.
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From page 122... ...
1960. Mechanisms of resistance to plant-parasitic nematodes, pp.
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From page 123... ...
Engineering computations for cost and efficiency are readily adaptable to pathogen control methods utilizing heat and are very useful if the biological aspects are given due consideration. Heat affects nematodes in many ways, ranging from immediate destruction by burning or searing at extremely high temperatures to the coagulation of cytoplasm at approximately 65°C, a relatively low temperature.
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From page 124... ...
Nematodes inside porous substrates can be reached by transferring heat throughout the substrate by agents such as hot water, steam, or perhaps hot air, or by crumbling and spreading the substrate into a thin layer to obtain exposed surfaces and then applying heat.
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From page 125... ...
Treatment of a moving and tumbling soil mass by dry heat assures uniform heat distribution. However, none of these methods is widely used.
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From page 126... ...
Scouring by flowing water, the force of steam, and brushing can be used with this method. Soil can be disinfested by moist heat, either as hot water or steam.
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From page 127... ...
Steamed, fine-textured soils become more granular, with resulting improvement in aeration and drainage. Increased plant growth sometimes results from increased availability of nutrients, improved physical structure of the soil, and, perhaps, from favorable biological changes, in addition to the benefits of pest and pathogen destruction.
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From page 128... ...
This is achieved by having present a large volume of water compared with the volume of plant materials being treated, having adequate heater capacity, or having additional hot water available to add to the bath for quick correction of temperature drops (see Figure 40, Chapter 8)
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From page 129... ...
A few examples of recommended hot-water treatments indicate the general range of temperature-time combinations found useful: narcissus bulbs infected with stem nematode (Ditylenchus dipsaci) , treat 4 hours at 43.5°C in 0.5 percent formalin in water; iris bulbs with the potato rot nematode (D.
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From page 130... ...
Electrical energy applied at radio-wave frequencies, similar to diathermy, killed encysted golden nematodes (Heterodera rostochiensis) located within bales of burlap bags.
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From page 131... ...
Although prospects of using irradiation to control nematodes do not appear promising, the different kinds of radiation, such as x rays, gamma rays, ultraviolet rays, and cathode rays, should be tested. CONTROL BY MISCELLANEOUS PHYSICAL FACTORS Physical methods, such as ultrasonics, osmotic concentration, mechanical destruction, pressure, desiccation, and mechanical seed-cleaning, have been insufficiently tested or have been found unfeasible.
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From page 132... ...
Chemical control has limitations and cannot completely replace crop rotation, fallow, and the use of resistant varieties. Interactions among soil, chemicals, and nematode pests are not yet well understood.
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From page 133... ...
The use of chloropicrin, another of the early soil fumigants, is limited by high cost and the need for a surface seal because of its relatively high vapor pressure. It is especially valuable where serious fungus and nematode problems occur in the same field.
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From page 134... ...
FACTORS INFLUENCING NEMATODE KILL IN SOIL Nematodes live in thin water films intimately associated with and surrounding soil particles. To be effective, nematocidal chemicals must penetrate and diffuse into pores or crevices in the soil to contact the nematodes and, in addition, must penetrate the moisture films surrounding the nematodes.
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From page 135... ...
SOIL TYPE The diffusion of volatile compounds is definitely influenced by soil type. Clay particles or organic matter may adsorb the compound and reduce the dispersion of the material.
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From page 136... ...
With increased clay content, soil moisture and temperature conditions should be more favorable before fumigation is attempted. APPLICATION DEPTH The depth at which volatile fumigants are applied varies with vapor pressure, dosage, temperature, moisture, soil type, nematode species to be controlled, and depth of control desired.
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From page 137... ...
Increased depth and rate of application are associated with high nematode kill to deep soil levels and little loss of vapors from the soil surface. If soil temperature is above 27°C and soil moisture is considerably below field capacity, depth of application should be increased and, to retain the vapors in the soil, the surface of the soil should be well compressed following application.
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From page 138... ...
The most common method of applying methyl bromide and chloropicrin, which are gases under field conditions, is by injection, after which water is sprinkled on as a surface seal or the soil is covered with a vapor-proof film or cover. Equipment is available which efficiently injects these volatile compounds and covers the soil surface with polyethylene tarps in one operation.
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From page 139... ...
Additional work on granular formulations is needed, especially with the more volatile materials. Nonvolatile compounds are best used as granules or liquids that can be spread on the soil surface and then mixed into the soil by rototiller or disk harrow.
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From page 140... ...
The chemical may be metered into the irrigation water by gravity flow or through a centrifugal pump. The gravity-flow technique is successful if the nematocide is introduced into water with sufficient agitation for thorough mixing, such as a drop over a weir or head gate, or when the water comes from a pipeline with sufficient force for mixing.
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From page 141... ...
APPLICATORS Injectors The first nematocidal chemicals used on a field scale were volatile liquids; consequently, the first applicators were adapted to apply these materials beneath the soil surface to prevent vapor loss to the atmosphere. Commonly used applicators are hand injectors and shank or chisel injectors.
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From page 142... ...
A simple, inexpensive method of metering liquid nematocides is by gravity flow through metering orifices or coils from a constant-head container. The constant-head container is a sealed vessel with the liquid outlet and air inlet located at the same level, near the bottom of the drum (Figure 50)
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From page 143... ...
The gravity flowmeter may be used with the chisel method of application (Figure 53)
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From page 144... ...
application, the entire area is treated, usually by chisel application at 12- to 14-inch spacing or, if the compound is nonvolatile, by spreading it uniformly over the soil surface and mixing it with the soil by disk or rototiller. With high dosage rates, to obtain deep penetration, down to 8 feet, the chisels may be as far as 18 inches apart.
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From page 145... ...
(Courtesy of Shell Development Company.) An important way to reduce the cost of soil fumigation is by row rather than over-all application.
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From page 146... ...
A strip or row preplant treatment can also be used for some perennial crops, such as peach, grape, citrus, and walnut, saving as much as 50 percent of the chemical as compared with over-all application. A disadvantage of this procedure is that recontamination from cultivation or irrigation is almost certain.
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From page 147... ...
POSTPLANT TREATMENT The application of chemicals to established plants for control of plantparasitic nematodes, especially root parasites, is a recent development, used mostly with perennial crops such as trees, vines, and certain ornamentals. Increased yields from postplant treatments usually occur only after the plant
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From page 148... ...
Two effective methods for applying nematocides to established plants include side-dressing with a chisel applicator or hand injector and application in irrigation water. If the land is level and the soil type is satisfactory, application by irrigation is preferred, because it is easy, requires little equipment, and coverage is uniform, especially close to vines or trees.
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From page 149... ...
It is doubtful whether a material can be found that will be effective on all plants and toxic to all stages of all species of plant-parasitic nematodes and that will also readily penetrate plant tissue, roots, bulbs, rhizomes, and corms without injury to the plant. The most difficult nematode species to control are the migratory endoparasites (Pratylenchus spp.
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From page 150... ...
A volatile compound capable of giving protection in the root zone could not be effective at the shallow depth of application necessary for a seed treatment. Volatile compounds must be applied 6 to 8 inches deep, while seed is usually planted less than 2 inches deep.
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From page 151... ...
A dynamic equilibrium can be established between the internal and external concentration of the nematocide in as short a period as 15 to 30 minutes, depending on the specific nematocide and the nematode species. The internal concentration of the nematocide may be from 2.5 to 20 times the external concentration.
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From page 152... ...
Because of the rapid rate of solvolysis in various solvent systems, including water, some organic halide nematocides show a lower order of toxicity than is consistent with their rate of reaction in bimolecular nucleophilic substitution reactions. Fortunately, allyl alcohol and some of the halogen-substituted allylic alcohols are very good nematocides; therefore, solvolysis is not always detrimental.
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From page 153... ...
Unfortunately, most of the data on this selectivity comes from field plots and consequently is confounded with many important physical and biological variables affecting the efficacy of nematocides. Differences occur in toxicity to various stages in the life cycle of a given nematode species and to species of various nematode genera.
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From page 154... ...
, are reported to have a high degree of selectivity for rootknot nematodes. Both are effective in controlling root-knot nematodes in soils at concentrations below 5 ppm, but neither is effective against numerous other plant-parasitic nematode species tested.
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From page 155... ...
Are they directly specific for certain nematode species or indirectly through the host plant, such as by repellent action? Can nematodes become resistant to nematocides?
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From page 156... ...
1950. The effect of soil type on the dispersion of soil fumigants.
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From page 157... ...
From the various control methods available, they must select the method that is the most effective, most economical, or both. The method selected will depend on the nematode species, the host plant, the environmental situation, the cash value of the crop, and the relative cost of available control methods.
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From page 158... ...
For example, diseases of a number of annual crops caused by the root-knot nematodes (Meloidogyne spp.) can be controlled by preplant soil fumigation.
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From page 159... ...
The effectiveness of preplant soil fumigation of soils planted to perennial crops has been judged on the basis of how closely nematode control approximates eradication. This reflected the long-term nature of the crop, the inability to rotate, and the lack of an effective nematocide that could be used for postplant treatment.
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From page 160... ...
In other states, such as Colorado and Utah, soil fumigation consistently results in profits to sugar-beet growers and is recommended. In California, soil fumigation for root-knot nematode control on sugar beets in the San Joaquin Valley is recommended, because the nematode drastically reduces the tonnage of roots produced and also affects the quality of the root and, consequently, the ease with which sugar is extracted.
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From page 161... ...
Root crops such as carrots, sweet potatoes, table beets, and white potatoes are markedly reduced in quality and in market acceptance by diseases caused by root-knot nematodes, even though the crop yield may not be materially affected. Cash returns on a crop of sweet potatoes are increased as much as $300 per acre from an expenditure of only $30 per acre for soil fumigation.
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From page 162... ...
In California, one of the oldest soil treatments is a mixture of methyl bromide and chloropicrin, which is applied, before planting, on a large proportion of the strawberry acreage at the rate of 300 pounds per acre, costing approximately $270. An estimated 10 million pounds of EDB are used annually in the United States for soil fumigation.
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From page 163... ...
With these nematodes, the level of infestation in the top 1 or 2 feet of soil is the primary concern. Reliable estimates of soil populations to depths of 8 to 10 feet or more are needed for many nematode species, particularly for those that are parasitic on deep-rooted perennials.
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